"Aw, a bloodhound, how cute!" reacted Sally to his choice.
"You don't think they're ugly?" said Jeff insecurely, relieved but somewhat surprised that Sally wouldn't judge him for wanting to try life as a wrinkly long-eared scent-detector, for potentially up to a few hours anyway.
"What? Of course not..." Sally tried to reassure him, rubbing her arm thoughtfully, deliberately neglecting to mention her life-long crush on a particular bloodhound that walked through the neighborhood daily as part of its owner's morning routine.
"Well, either way, that's my choice," confirmed Jeff with a shrug. "I've always thought bloodhounds were cool dogs. No offense, of course--I obviously love labs, too."
Sally smiled and turned back to the computer. Jeff felt a sudden tumbling feeling in his ears, which then felt old bent and seemed to be swinging slightly after their surprise tumble.
"Wow! Your dog ears formed fast!" exclaimed Sally. Jeff reached up to touch one, only to feel a flat, slightly fuzzy surface that made him feel like he was touching the back of his left earlobe. That feeling continued for Jeff as he traced the floppy blanket of fuzz down to its ending near his chest. Soon he was gripping both ears and flapping them around with both hands, amused by how it felt to have such things hanging from his face. Then his ear canal popped, and he could hear Sally's heartbeat, the ticking of the living room clock, the sound of human voices in the next house over, and the barking of dogs several blocks away. The whirring of the computer's internal fan blades sounded like the roar of a gym fan to his sensitive bloodhound ears. He had to take a deep breath to bring himself back down to earth.
"Wow, I never really understood how much dogs can hear before," Jeff mused.
"It's alright. We know humans are deaf because you always treat us like we bark at nothing," giggled Sally.
Jeff was still playing with his hound ears when, all at once, his body tensed up an unexpected tsunami of sensation nearly washed him away, so to speak. He had to be careful not to tug the ears out of his skull because they were still in his hands when it happened. He wasn't quite sure what it was at first, because it was so intense and so unlike any sensation he recognized from being human. After a moment's thought, he managed to narrow down the source of the sensation to his face, and then more specifically to his nose. He felt and heard himself whine and saw Sally gain a concerned expression on her human face. At last, he managed to recognize the sensation as a smell, in which he could then identify enough details to realize that it was more than one smell--indeed, more than a dozen smells, more than a hundred maybe.
Having been conditioned by life as a human to largely ignore the way things smell, and to assume that one's inability to do so implies that something "stinks", Jeff clamped his nostrils shut with his fingers, trying to shield himself from the onslaught. It was no use, though, as his nose began to twitch, moisten, expand too fast for his fingers to easily keep up. His mouth seemed to be growing with it (he could feel his tongue stretching inside him). Trying to breathe through his mouth, he was surprised by how low his tongue was hanging even under his faraway chin. Even breathing through his mouth forced him to smell things after his Jacobson's organ came online. Staring down the long, broad bridge of his nose (the top of his muzzle!) made Jeff really stop to think about the complex olfactory machinery he would be carrying around during his time as a dog, especially one known for its sense of smell even compared to other dogs. He emptied his lungs, reeled his slobbery tongue back in, closed his mouth as well as a bloodhound can hope to close it, and deliberately took another breath in through his glistening nostrils.
"Master!" Sally said, jumping up and reaching toward him, watching Jeff stumble for a moment as though he were going to pass out. Jeff barely heard her even through those new ears of his. He managed to prop himself up using a small table, but he still appeared somewhat dazed. For a second or two, Jeff almost forgot who and where he was while human brain scrambled to accept some more massive downloads from a nose 20, 30, 40 times more sensitive than what it had before, more acute than even most dogs will ever have access to. Fortunately, the machine was already getting to work on Jeff's brain, too, filling him with a new instinct to quite literally follow his nose.
Jeff sniffed the air silently for a few seconds and then tore through the blankets of his bed, the contents of his (actually now Sally's) closet and sock drawer, sniffing everything he could find before dropping his nose to the floor and following scents around in circles to try to make sense of them. He tried to apologize (impossible with his new mouth) before sticking his nose right up Sally's ass to get a reading on her. She jumped, and Jeff jumped up and landed with his hands on the desk and started sniffing they keyboard, finding his and Sally's fingerprints on it by scent. At last, the boy with the bloodhound muzzle relaxed, flopped down on the floor on his back, drank in the scents and sounds around him once more, and felt like he could take a nap after his little escapade.
"Are ... are you okay, boy?" asked Sally, not having fully anticipated how Jeff's transformation would affect him. In response, both Jeff and Sally heard a gentle thumping sound on the floor between Jeff's legs. Jeff finally appreciated just how much his mind had changed: he hadn't even thought to smile or say he was fine. Instead, his impulse was to wag his tail. He hadn't even noticed he had grown a tail, because he had been so focused on his nose at the time! The new appendage was sticking awkwardly out of his shorts, which were getting uncomfortable as his leg anatomy changed. His arms and chest were starting to have form an independence movement within his shirt, too, as his torso and shoulder anatomy went through analogous changes. Jeff whined, and Sally helped him get out of those ridiculous garments that had no place on an animal. Relieved, Jeff rolled over and launched himself into a standing position on all fours, wagging his long tail and sniffing around a little more, less desperately this time. He saw his new Sally standing in front of him with a thrilled look on her face, heard her say something he didn't understand, and pranced forward to get closer to her.